Medical terms A–Z

The person chosen in advance to speak for a patient who can no longer speak, and the document that appoints them.

In a clinical study, a person who does not have the disorder or disease being studied.

The muscle of the heart starves while the person is usually awake and talking, which is what separates it from a cardiac arrest.

Tumors that spread to the heart from cancer elsewhere in the body are considerably more common than cancer that originates in the heart itself.

A name that frightens more than it explains: the heart has not stopped, it has fallen behind what the body asks of it.

Most murmurs are harmless noise from normal blood flow, which is why the character of the sound matters more than its presence.

The name is a misnomer, and the overlap with chest pain from the heart is exactly why the two are so often confused.

Molecular chaperones named after the heat experiment that revealed them, though they work constantly and not only in a crisis.

An herb used in traditional Chinese medicine to treat certain medical problems.

A detailed picture of areas inside the body.

A type of therapy in which radiation is aimed at a tumor from many different directions.

A type of bacterium that causes inflammation and ulcers in the stomach or small intestine.

A type of immune cell that stimulates killer T cells, macrophages, and B cells to make immune responses.

A protein found in the outer coat of paramyxoviruses.

A type of cancer involving blood vessels and soft tissue.

A rare cancer of the cells lining blood vessels, which is why it can begin almost anywhere in the body.

Originating in the blood or spread through the bloodstream.

A cancer of the blood or bone marrow, such as leukemia or lymphoma.

The specialist called when a routine blood count stops making sense, whether the answer turns out to be cancer or not.

A bruise stains the tissue, while a hematoma occupies space, and the trouble it causes comes mostly from what it presses on.

Every red cell, white cell and platelet traces back to one kind of stem cell, replaced constantly because none of them last.

A group of proteins that causes blood cells to grow and mature.

Tissue in which new blood cells are formed.

A drug used in photodynamic therapy that is absorbed by tumor cells.

Color is a poor guide here, since beets and some medicines redden urine while a serious cause may leave it looking normal.

The iron-holding ring that lets blood carry oxygen, and the same ring that turns a bruise yellow as it is dismantled.

A condition in which one side of the body or a part of one side is larger than the other.

An operation to remove one side of the larynx (voicebox).

A condition in which the body takes up and stores more iron than it needs.

Four protein chains around four iron atoms, arranged so that picking up one oxygen molecule makes the next three easier to catch.

Hemophagocytic lymphohistiocytosis is a rare, life-threatening syndrome of overwhelming immune activation that damages organs and destroys blood cells.

Bleeding is not faster than usual, only harder to stop, because the clot that forms is too fragile to hold.

In heavy bleeding it is the flooding of the airways, not the volume of blood lost, that does the damage.

In medicine, loss of blood from damaged blood vessels.

An enlarged or swollen blood vessel, usually located near the anus or the rectum.

Fast on, fast off and reversible with an antidote, which is why hospitals reach for it when clotting risk may change within hours.

Hepatectomy removes part or all of the liver, often performed to treat tumors, donate a liver segment, or address severe injury.

Hepatic describes anything relating to, affecting, or associated with the liver, including its blood vessels, tissue, and function.

A procedure to deliver chemotherapy directly to the liver.

A block in blood flow to the liver.

The major blood vessel that carries blood to the liver.

The vein that carries everything absorbed from the gut straight to the liver before the rest of the body sees it.

A condition in which some of the veins in the liver are blocked.

One word covering many diseases: the letter attached to a viral hepatitis says far more about its course than the word itself does.

A liver virus whose outcome turns less on the virus itself than on the age of the person it first infects.

Hepatitis C virus is a bloodborne virus that infects the liver, often persisting for years and gradually causing scarring if left untreated.

A virus too incomplete to infect anyone by itself, dependent on hepatitis B to supply the coat it cannot build.

First noticed as a puzzling new marker in liver cells of people with hepatitis B, later shown to be a separate virus.

A liver virus carried by contaminated water and by undercooked meat, usually brief but dangerous in late pregnancy.

A virus that may be found in patients with hepatitis (inflammation of the liver).

Having to do with the liver, bile ducts, and/or gallbladder.

A tumor of immature liver tissue in very young children, and among the more treatable childhood cancers when caught early.

Hepatocellular carcinoma is the most common primary liver cancer, arising directly from liver cells and closely linked to cirrhosis and chronic viral hepatitis.

A hepatocyte is the main parenchymal cell of the liver and carries out many of the organ’s metabolic, synthetic, and detoxifying functions.

Hepatoma is an older, imprecise term for a liver tumor and has often been used to mean hepatocellular carcinoma.

Hepatomegaly is enlargement of the liver beyond its expected size.

The protein found on the surface of some cells and to which epidermal growth factor binds, causing the cells to divide.

A protein involved in normal cell growth.

An herb used in traditional Chinese medicine to treat certain medical problems.

Herbal describes products or remedies derived from plants, which can carry measurable pharmacologic effects and interactions despite a natural origin.

A type of medicine that uses roots, stems, leaves, flowers, or seeds of plants to improve health, prevent disease, and treat illness.

Plant products sold under food rules rather than drug rules, which is what makes their strength and contents so variable.

A herbicide is a chemical formulated to kill unwanted plants, and exposure to certain herbicides can also cause toxicity in humans.

Present from the first cell onward, even when nothing shows for decades, and never the same claim as present at birth.

A gene change in a body's reproductive cell (egg or sperm) that becomes incorporated into the DNA of every cell in the body of the offspring.

Families share more than genes, and separating the inherited from the merely shared is the harder half of reading a family history.

The bulging of an internal organ through a weak area or tear in the muscle or other tissue that holds it in place.

A substance made from morphine.

A herpesvirus is any member of a large family of viruses that establish lifelong latent infection in the body after initial exposure.

A chemical that is formed when meat, poultry, or fish is cooked at high temperatures, such as frying, broiling, and barbecuing.

One word doing three jobs, in radiology, pathology and research, and the reason a single sample can misrepresent a whole tumor.

Derived from a different source or species.

Derived from a different source or species.

A substance being studied in the treatment of some types of cancer.

A substance being studied in the treatment of some types of cancer.

A type of virus that causes herpes infections and has DNA as its genetic material.

A type of herpesvirus that may cause Kaposi sarcoma (a rare cancer that can cause skin lesions) and a type of lymphoma (cancer that begins in the lymph system), especially in patients who have a…

Sound focused the way a magnifying glass focuses sunlight, burning a target inside the body without cutting the skin.

Nothing is usually felt, so damage to the vessels of the eyes, kidneys and brain accumulates long before anything announces it.

More glucose circulating than the body can move into its cells, a state with several causes besides diabetes.

A term used to describe cells that look abnormal under a microscope.

An intensive drug treatment to kill cancer cells, but that also destroys the bone marrow and can cause other severe side effects.

A phrase that runs three separate ideas together, total amount, delivery speed and number of sessions, which is how its abbreviation misleads.

A type of radiation therapy that uses high-energy photons (units of light energy).

A type of lymphoma that grows and spreads quickly and has severe symptoms.

A procedure in which high-energy sound waves are aimed directly at an area of abnormal cells or tissue in the body.

Cancer that is likely to recur (come back), or spread.

Hilar describes the hilum, the specific point where vessels, nerves, and airways or ducts enter and exit an organ.

Four different receptors explain how one small molecule can cause hives, drive stomach acid, and keep the brain awake at once.

A substance being studied in the treatment of some types of cancer and other conditions.

An outdated term referring to non-Hodgkin lymphomas made up of large abnormal lymphoid cells.

The examination of tissue specimens under a microscope.

Architecture is the point: how cells sit relative to one another often says more than how any single cell looks.

Packing is only half the point, since how tightly DNA is wound decides which genes can be reached and read.

An enzyme that removes a small molecule called an acetyl group from histones (proteins found in chromosomes).

A drug that leaves chemical tags in place on the spools DNA winds around, changing which genes a cell can reach.

The study of diseased cells and tissues using a microscope.

A research study in which the medical records of groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke and those who do not…

An individual treated in the past and used in a comparison group when researchers analyze the results of a clinical study that had no control group.

A virus that disables the very cells sent to fight it, so the damage appears as other infections rather than its own illness.